AP Computer Science Wiki

In java, there are some signs that are used as simple codes that make it look simpler and allow us to do less typing.

|| ----> or (Usually used in if statement)
EX.

if(x == 0 || x ==1)    //This means if x equals to 0 or 1, x equals five.
{                      //You cannot do if(x == 0 || 1), because it will cause an error.
   x = 5;
}

&& ----> and (usually used in if statement)
EX.

if(x > 0 && x < 10);   //This means if x is greater than 0 and less than 10, x equals five.
{                      //You cannot do if(x > 0 && < 10), it will cause an error.
     x = 5;
}

! ----> opposite
EX.

private boolean isAlive = true;  //Makes a boolean variable called isAlive which is set to true.
...
isAlive = !isAlive;  //Now isAlive is set to false because isAlive(true) equals to the
                       //opposite of isAlive(false).
                     //another way to think of this is !isAlive is the same as saying is-"Not"-Alive.

< ----> less than

----> greater than

EX.

if(x < 0)  //means if x is less than 0, x equals -1.
{
     x = -1;
}

<= ----> less than or equal to
>= ----> greater than or equal to
EX.

if(x <= 0)  //Instead of using < with line under it, in java, you use <=.
{
    x = -1;
}

= ----> equal to (stored into)
EX.

x = y;  // x is equal to y (y is stored into x)

== ----> if equal to (only used in if statements)
EX.

if(x == 0)  //If x is equal to 0, x is 0.
{
    x = 0;
}

De Morgan's law has two forms: one for the negation of an and expression and one for the negation of an or expression.
Example:
!(a && b) is the same as !a || !b
!(a || b) is the same as !a && !b

According to the above equalities, choose the correct answer to the following question.

What is the equiavalent to the following....... : ! (( x <= y) && (y > 5))
a. (x <= y) && (y > 5)
b. (x <= y) || (y > 5)
c. (x >= y) || (y < 5)
d. (x > y) || (y <= 5)
e. (x > y) && (y <= 5)

The ! distributes to the equations and the && so one can immediately eliminate answers A and E. !(x < = y) would change the equation to (x > y) so the only possible answer would then be D.

Sign Code